German Patent No. 1 95 13 156 describes an internal combustion engine, composed of two cylinder banks, in which each cylinder bank has its own exhaust-gas turbocharger. By controlling the exhaust-gas turbines arranged in the exhaust trains of the two cylinder banks, the boost pressure in the shared intake train of the two cylinder banks is controlled to a setpoint value. If at this point, a fault occurs in one of the two exhaust trains, for example, the catalytic converter becomes clogged, or there is a defect in the boost pressure controller, or a malfunction of the exhaust-gas turbine, etc., this becomes noticeable by different rotational frequencies of the two exhaust-gas turbochargers. Namely, the control circuit will compensate for the system deviation of the boost-pressure actual value compared to the boost-pressure setpoint value, caused by the fault occurring on one side, by an upward adjustment of the turbocharger on the fault-free side. In so doing, the rotational frequency of the turbocharger can reach a critical value which results in its destruction.
To rule out the destruction of a turbocharger in the event of a fault, according to German Patent No. 195 13 156, provision is made for a fault-detection device which, when it detects a fault on one side in one of the two exhaust trains, interrupts the closed-loop charging control and switches over to an open-loop control. The open-loop control is designed in such a way that the turbocharger does not enter into its critical rotational-frequency range. For example, the fault-detection circuit detects engine misfirings in the two cylinder banks. In so doing, it determines the rate of occurrence of engine misfirings for the individual cylinder banks and, if the rate of occurrence exceeds a predefined limiting value, it signals that a fault exists on one side in one of the two exhaust trains.
A longer time can pass until a defect in one of the two exhaust trains leads to engine misfirings in one of the cylinder banks, during which time the control circuit will already have adjusted one of the two exhaust-gas turbochargers into a critical rotational-frequency range. Therefore, an object of the present invention is to provide a method and a device for monitoring the functioning of two exhaust-gas turbochargers that belong to two separate cylinder banks of an internal combustion engine, which makes it possible to detect a defect in one of the exhaust trains as quickly as possible, so that appropriate protective measures can be initiated for the turbochargers.